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John M. Foley; Forward–backward masking of contrast patterns: The role of transients. Journal of Vision 2011;11(9):15. doi: https://doi.org/10.1167/11.9.15.
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© ARVO (1962-2015); The Authors (2016-present)
Graham and Wolfson have shown that, after adaptation to an array of Gabor patterns, observers discriminate poorly between spatially identical Gabor arrays in which the contrasts are symmetrically above and below the adapt contrast. Ten experiments are reported that show that the effect occurs in simple contrast discrimination tasks and examine its properties using a two-alternative spatial forced-choice paradigm. The experiments show that the effect is quite robust and manifests itself in several different experimental paradigms. It occurs with masks as short as 50 ms, but it disappears when an interval as short as 30 ms intervenes between the test patterns and the masks. It occurs at 4 and 8 c/deg. The decrease in discrimination for straddle contrasts is accompanied by an increase in discrimination for contrasts above the mask contrast. A model is presented that describes and predicts the results. The key idea of the model is that patterns which suddenly change contrast produce two responses in the visual system, a V-response that is a function of the absolute value of the difference between the test contrast and the mask contrast and an S-response that is an increasing function of contrast.
Notes: S Et and σ were fixed throughout at 100 and 1.11, respectively. In these fits, sometimes there is a valley in the error space along which RMSE varies less than 1%. In those cases, p was fixed at 2.6. For Experiment 1, SSE and RMSE are given in decibels, since error in decibels was minimized in these fits as is common for TvC data. For Experiment 9 (8 c/deg), S Im is higher than for 4 c/deg. For Experiment 10 (straddle condition), fit is to S-response model. Most of the data sets for each observer are fitted with the same five parameters. The C m factor for ATB (Experiment 7) is the factor multiplied by the mask contrast to give effective mask contrast.
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